The trial of Paul Manafort began yesterday in federal court in Virginia. It has received broad coverage because, at one point, Manafort was the Trump campaign chairman and he is being prosecuted by the Mueller team conducting an investigation of President Trump.

And yet, it really has nothing to do with anything.

Manafort is charged with a variety of tax and banking crimes. The trial is important to him because if convicted, he faces some serious time in the federal pen. But these charges have nothing to do with the Trump campaign, Russian interference with the election, or really anything else that anyone not named Paul Manafort would care about.

So why are they being brought by the special prosecutor?

It has to do with a kind of “drive-by” authority that is often given to special prosecutors and was given to Mueller. Basically, if in the course of his investigation of President Trump he came across other crimes, he was given the power to prosecute them. Apparently, while investigating Manafort, this is exactly what happened.

Of course, Mueller could have just handed off this tax and banking case to one of the many regular prosecutors who do this all the time, but he has chosen not to do so. (In the interests of full disclosure, I worked with and for Mueller in the U.S. Attorney’s Office back when dinosaurs roamed the earth.)

This is, I think, a questionable decision. First, as is evident from the coverage, it tends to confuse many people into thinking that this trial has something to do with his core investigation. Win or lose, everyone will read the result as bearing on whether the president did or did not do what he is accused of.

Second, it distracts from the core investigation. If the leader of the free world is investigated while in office, it should only be done by someone equal to the task. When Mueller was designated to be a special prosecutor, it was because his career, particularly his time as director of the FBI, gave him that gravitas. But this special authority should not be wasted on garden-variety prosecutions that are outside his core task.

Most problematic, however, is the taint it will give to any future testimony that Manafort gives. The fact that Mueller and his office are prosecuting the case makes it appear that they are trying to get leverage against Manafort. Perhaps they are. But it means that anything he ever says will look like it was the result of pressure and will be discounted heavily. Indeed, if there is a conviction, it will be the testimony of a felon.

So Mueller gets a prosecution and possible conviction, but undermines his main mission. That is a bad exchange.

Evan Slavitt is a Massachusetts lawyer who writes on legal issues for the Herald.